WiremanWireman · Transfer switch won’t transfer: troubleshooting for electricians · 2023 NEC ·
Transfer switch won’t transfer
Is the generator source acceptable to the switch, are timers running, and is the switch able to move?
Before you start
How much electrical experience do you have?
This sets how much detail each step shows. You can change it any time.
Showing detail
How it works
An automatic transfer switch (ATS) watches the normal (utility) source. When it drops out, the controller starts the generator, waits until generator voltage and frequency are acceptable and any warm-up delay has passed, then moves the load to the emergency source. When utility returns, it waits a retransfer delay, moves back, and lets the engine cool down. Many “won’t transfer” calls are a timer that hasn’t finished or a source the controller doesn’t consider acceptable.
Every question and answer in this guide. Tap “Step by step” to walk through it.
- Which way won’t it go?
- Won’t transfer to the generatorIs the generator running, and is its output breaker on?
- Not runningThe generator didn’t start
- Running, breaker off or trippedGenerator output breaker is off
- Running, breaker onTest: Measure the emergency source at the ATSExpect: Rated voltage within about 10% and close to 60 Hz, with the controller showing the emergency source available.
- No voltage at the ATSOpen feeder between the generator and the ATS
- Voltage or frequency out of rangeGenerator output outside the ATS’s pickup settings
- Good, but no transferIs the controller in automatic, with no inhibit, test or fault showing, and has the transfer delay passed?
- Wrong mode, or a delay still runningIt’s waiting on a timer or a mode setting
- Auto, no delay, still no transferTransfer mechanism or controller failure
- Won’t go back to utilityTest: Measure the normal source at the ATSExpect: Normal utility voltage on every phase, and the controller showing normal available.
- A phase missing or lowUtility source not fully back
- Normal, timer still countingIt’s waiting on a timer or a mode setting
- Normal, no timer, won’t moveTransfer mechanism or controller failure
- Won’t transfer to the generatorIs the generator running, and is its output breaker on?